Should soy stay or should it go? When my children were young, we discovered they were allergic to cow’s milk. I switched them to soy. Now, when I see headlines describing the dangers of soy, I wonder whether I did them a great disservice.
Soy is present in many prepared foods. It’s eagerly embraced by some adopters of a plant-based diet because it is filled with high-quality protein and nutrients including B vitamins, fiber, potassium, and magnesium. Soy protein contains all nine essential amino acids that the body cannot make on its own making it a “complete” protein. These facts make soy sound like a great food.
But, like eggs, soy has its detractors. Some animal studies have shown that high dosages of isoflavone or isolated soy protein extracts tend to stimulate breast cancer growth. Isoflavones are phytoestrogens that function similarly to human estrogen (a hormone) but with weaker effects. Isoflavones may also alter the behavior of estrogen receptors thereby affecting hormone balance.
Hormone balance affects mood, libido, weight, sleep quality, and energy levels. Life is both healthier and more pleasant when we maintain the proper balance. Any alteration of hormone balance through intentional disruption brings risks whether it’s hormone-based birth control, hormone replacement therapy, or dietary estrogens.
A study of 3700 Japanese-American men in Hawaii who consumed large amounts of tofu during middle-age showed a significant association with greater cognitive impairment and brain atrophy in late life compared with men with the lowest tofu intakes. On the flip side, a study of Asian women showed that soy foods sometimes reduced the risk of breast cancer.
In fact, there are numerous soy studies with conflicting results. At a glance, it’s hard to determine whether soy contributes to or reduces the risk of breast cancer. The relationship with dementia is not certain either.
Soy foods are not the only foods that contain phytoestrogens or dietary estrogens. Flaxseeds, sesame seeds, sunflower seeds, almonds, walnuts, apples, cranberries, grapes, pomegranates, strawberries, carrots, lentils, yams, mung beans, sprouts, barley, oats, wheat germ, coffee, bourbon, beer, red wine, and olive oil all contain phytoestrogens. We don’t think of most of those as harmful, but all phytoestrogens are not created equal or used by the body in the same way.
More than likely, there are many factors that determine whether soy will detrimentally affect you–ethnicity, hormone levels, type of soy, age and frequency of ingestion, interaction with medications, etc. With no definitive way to know whether phytoestrogens put you at risk, it is probably best to consume soy in moderation.
If you choose packaged foods, be sure to read the labels. You’ll often find soy in unexpected places. If you are eating a plant-based diet, you may want to limit tofu. And with all of the non-dairy milk options, there’s really no reason to rely on soy.
When you do eat soy, less processing is always better. I love edamame. Every few months I’ll have some for dinner two or three times in a week. Then I don’t think about it again for months.
With no consistent, definitive science to rely on at this time, consuming soy has to be a matter of choice. For now I’m choosing stay, but in deliberate moderation. Only time will tell whether my choices will harm my children or me. In the meantime, I’ll probably keep asking: Should soy stay or should it go?
The following is an extensive review of soy research. Please be aware that it was funded by The European Soy and Plant-based Foods Manufacturers Association, and the author is the executive director of the Soy Nutrition Institute, an organization funded by the United Soybean Board and its soy industry members.